As no one has answered you yet, I'll provide what information I know as non-expert who checked out realtor.com and consumerfinance.com
Prequalified - you provided data about your income, debt, assets.
Preapproved -- a lender actually VERIFIED your income, debt, assets and actually runs a credit check.
- [this counts as a hard inquiry to your credit report and can affect your score, so don't go overboard getting preapproved by every lendor you can find. I've seen an online mention that hard inquiries within a short timeframe are bundled together and only hit your score once, but I haven't been able to independently verify that, so I'm planning for the worst and only looking at 2-3 lendors.]
- Your loan is submitted for preliminary underwriting (typically 24 hour turnaround). After it passes preliminary underwriting, your mortgage consultant sends you with a preapproval letter that defines the amount they are prepared to loan you.
- Preapprovals are only good for a specific window of time.
